How to Inject Map having dependent Object in value using Spring dependency injection by constructor?

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Introduction

In Spring Framework applications, configuring collections via constructor injection allows beans to remain immutable and completely initialized upon creation. A frequent use case involves mapping a basic identifier (like a String or Integer key) to a custom dependent object as the map value.

In this guide, you will learn step-by-step how to inject a Map having a simple key and a dependent object as its value using constructor dependency injection in Spring XML configuration.

1. Create the Dependent Class (Fruit)

First, define the dependent object class (for example, Fruit) that will serve as the value inside our map:

public class Fruit {
    private String name;
    private int price;

    public Fruit(String name, int price) {
        this.name = name;
        this.price = price;
    }

    @Override
    public String toString() {
        return "Fruit [name=" + name + ", price=" + price + "]";
    }
}
  

2. Create the Target Class (FruitShop)

Create the target class FruitShop that receives a Map<String, Fruit> through its constructor:

import java.util.Map;

public class FruitShop {
    private String shopName;
    private Map<String, Fruit> fruitMap;

    public FruitShop(String shopName, Map<String, Fruit> fruitMap) {
        this.shopName = shopName;
        this.fruitMap = fruitMap;
    }

    public void displayFruitShopInfo() {
        System.out.println("Shop Name: " + shopName);
        for (Map.Entry<String, Fruit> entry : fruitMap.entrySet()) {
            System.out.println("Key: " + entry.getKey() + " -> Value: " + entry.getValue());
        }
    }
}
  

3. Configure Spring XML with <entry key="..." value-ref="...">

In your applicationContext.xml, declare the dependent Fruit beans and inject them into the target bean's map using the value-ref attribute:

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans 
       http://www.springframework.org/schema/beans/spring-beans.xsd">

    <!-- Dependent Beans -->
    <bean id="appleBean" class="Fruit">
        <constructor-arg value="Kashmiri Apple" />
        <constructor-arg value="120" />
    </bean>

    <bean id="mangoBean" class="Fruit">
        <constructor-arg value="Alphonso Mango" />
        <constructor-arg value="250" />
    </bean>

    <!-- Target Bean -->
    <bean id="fruitShop" class="FruitShop">
        <constructor-arg value="Green Valley Mart" />
        <constructor-arg>
            <map>
                <entry key="fruit_1" value-ref="appleBean" />
                <entry key="fruit_2" value-ref="mangoBean" />
            </map>
        </constructor-arg>
    </bean>

</beans>
  

4. Test the Application

Load the application context and execute your application:

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        FruitShop shop = (FruitShop) context.getBean("fruitShop");
        shop.displayFruitShopInfo();
    }
}
  

Watch More Spring Tutorials

• Understanding Constructor Injection Type Ambiguities in Spring | Spring Framework Explained
• In-Depth Comparison: Constructor Injection vs. Setter Injection in Java | Spring Tutorial
• Dependency Injection Fundamentals: Constructor vs. Setter Injection | Spring Tutorial

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How to Inject Map having dependent Object in value using Spring dependency injection by constructor?

How to Inject Map having dependent Object in value using Spring dependency injection by constructor?

How to Inject Map having dependent Object in value using Spring dependency injection by constructor?

How to Inject Map having dependent Object in value using Spring dependency injection by constructor?

How to Inject Map having dependent Object in value using Spring dependency injection by constructor?